Meet Kaitlin Olson and Rob McElhenney's Son Leo Grey!

It's Always Sunny in Philadelphia costars Kaitlin Olson, 36, and Rob McElhenney, 34, welcomed son Leo Grey April 5 at their home in L.A. and four days later, the couple posted the very first pic of their bundle of joy.

"Leo Grey McElhenney…born April 5th after 23 very very long hours," Olson tweeted late Monday. "We're in love."